In operating conventional cameras of the prior art, the user is unable to determine whether he has properly loaded the film in the camera and, if he has not, he may find to his chagrin that after supposedly taking a full roll of pictures, he has taken no pictures at all. In some cases, he may discover the improper loading of the camera when attempting to rewind the film or when unloading the camera. In other cases, he may not be aware of any problem at all until after the film has been developed and he may not then be able to ascertain the cause of the trouble and may make incorrect assumptions with respect to the quality of the film or the operability of the camera mechanism.
Various arrangements have heretofore been proposed for avoiding this problem but such arrangements have not been used to any great extent, if at all, due to problems with reliability, complexity and cost of manufacture. In certain proposed arrangements, indicators have been operated by movement of film on a take-up spool or between supply and take-up spools but such arrangements are not entirely reliable because they require attention on the part of the user of the camera. Other proposed arrangements require electrically operated shutters and switch arrangements, and/or other complex mechanisms for preventing operation of the shutter when film is not advanced. Such arrangements are not only complex but they are expensive and can be unreliable as well.
Proposals have also been made for providing mechanisms which prevent rotation of a take-up spool or otherwise prevent film movement when no cartridge is in place in the camera. Such proposals do not recognize and do not solve the problem presented when the user fails to properly thread the film and attach the film to the take-up spool. They do not recognize that if, for any reason, the film is not connected to the take-up spool, the camera will not move the film through the image area at the back of the exposure chamber. Thus, the user can operate the camera without being aware that the film is not being advanced and that no pictures are being taken.